Steam reforming of a hydrocarbon to manufacture syngas is a process in which the hydrocarbon and an oxygen source are supplied to an autothermal reformer. The combustion reaction is exothermic and supplies the heat needed for the catalytic reforming reaction that occurs in the autothermal reformer, which is endothermic, to produce a relatively hot reformed gas. The hot gas from the autothermal reformer is then used as a heat source in the reforming exchanger, which is operated as an endothermic catalytic steam reforming zone. In the reforming exchanger, a feed comprising a mixture of steam and hydrocarbon is passed through catalyst-filled tubes. The outlet ends of the tubes discharge the endothermically reformed gas near the shell side inlet where it mixes with the hot gas from the autothermal reformer. The hot gas mixture is then passed countercurrently across the tubes in indirect heat exchange to supply the heat necessary for the endothermic reforming reaction to occur.
Reforming exchangers are in use commercially and are available. Various improvements to the reforming exchanger design have included, for example, the tube bundle support and low pressure drop tubes.
A need exists for improving the basic reforming exchanger design to minimize the capital cost of the equipment. Current reforming exchanger design uses expensive alloys in the construction the tube bundle and tube sheets since the reforming exchanger are used at relatively high operating temperatures and pressures.
A need exists for improving the basic reforming exchanger design to maximize the capacity of the reforming exchanger within the practical limits of fabrication capabilities. Further, if the size and weight of the reforming exchanger is minimized, maintenance operations that require removal of the tube bundle will be facilitated.
One approach to reducing the capital cost and increasing the capacity of the reforming exchanger is to increase the ratio of surface area to volume of the reactor tubes. By decreasing diameter of the tubes and using monolithic catalyst structures in the reforming exchanger design, the capital costs are decreased and/or the capacity is increased with respect to the tube bundle.
A need for similar improvements to the shell-side of the reforming exchanger, especially improvements that can maintain and improve the advantages of the small-diameter tubes. Previous designs have usually utilized a minimum of five shell-side cross passes with no tubes in the baffle windows. Five cross-flow passes in tube bundles can result in an excessive shell-side pressure drop in some instances. While fewer passes can be used to reduce the shell-side pressure drop, the resulting reforming kinetics could be uneven due to an uneven shell-side temperature profile.
The embodiments are detailed below with reference to the listed Figures.